package com.ocom.common.utils;

public class SnowUtil {

    /**
     * 起始的时间戳
     */
    private final static Long START_STMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static Long SEQUENCE_BIT = Long.valueOf(12); //序列号占用的位数
    private final static Long MACHINE_BIT = Long.valueOf(5);   //机器标识占用的位数
    private final static Long DATACENTER_BIT = Long.valueOf(5);//数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static Long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
    private final static Long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static Long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static Long MACHINE_LEFT = SEQUENCE_BIT;
    private final static Long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static Long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private Long datacenterId;  //数据中心
    private Long machineId;     //机器标识
    private Long sequence = 0L; //序列号
    private Long lastStmp = -1L;//上一次时间戳

    public SnowUtil(Long datacenterId, Long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     *
     * @return
     */
    public synchronized Long nextId() {
        Long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT             //机器标识部分
                | sequence;                             //序列号部分
    }

    private Long getNextMill() {
        Long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

    private Long getNewstmp() {
        return System.currentTimeMillis();
    }

//    public static void main(String[] args) {
//        SnowUtil snowFlake = new SnowUtil(2, 3);
//
//        Long start = System.currentTimeMillis();
//        for (int i = 0; i < 1000000; i++) {
//            System.out.println(snowFlake.nextId());
//        }
//
//        System.out.println(System.currentTimeMillis() - start);
//
//
//    }
}